The investigators suggest that insertion of the "extra" DNA sequences into the X chromosome apparently turns on a gene, likely SOX3, located near the insertion site. SOX3 is a strong candidate because other members of this gene family have been shown to play a role in hair growth.
In addition, the insertion has occurred within a block of DNA sequence called a "palindrome," in which the sequence of the four building blocks of DNA (akin to letters of the alphabet) read exactly the same as their complementary sequences, but in the reverse direction. The particular palindrome at the site that the researchers studied is only found in humans.
"We don't yet know the significance of the palindromic sequence in this case," Patel said. "But it appears to be unstable, and can be entirely absent in many individuals with normal hair growth. It's only when there is insertion of certain chromosome segments at this site that people have extra hair."
Earlier, researchers had theorized that the CGH mutation is "atavistic" a trait that reappears after being absent for a long time. One example of an atavistic trait is extra nipples in both men and women.
"It's like the information is there in the genome, but is silenced," Patel said. "Then somehow it's reactivated, and can manifest as the trait. We don't know yet if this is the case with CGH."
Further studies will test if this is indeed true. "If in fact the inserted sequences turn on a gene that can trigger hair growth, it may hold promise for treating baldness or hirsutism [excessive hair growth] in the future, especially if we could engineer ways to achieve this with drugs or other means," Patel said.
|Contact: Leslie Ridgeway|
University of Southern California